Solvent treating of petroleum fractions



Oct. 17 1961 F. H. KANT 3,004,915

SOLVENT TREATING OF PETROLEUM FRACTIONS Filed Dec. 30, 1959 Z 9 m n 3 =5 Q 0 m l Z LIJ O gm 2% E o g a: LI- 0 (D O o LIJ N x o m LU'E' 3 3 FREEZING ZONE EXTRACTION TOWER FILTER \nvenror Fred H. Kom

Patent Attorney U ed States Pa e 1 SOLVENT This invention relates to improved process for the solvent extraction of liquid petroleum oil fractions to to Esso Research a corporation of Delaware bility of the aromatic separate their aromatic constituents from their paraflinic I constituents. The invention is particularly directed to improvements in the refining of lubricating oil fractions by phenol extraction.

The use of various selective solvents for refining petroleum oils is well known. In the treatment of lubricating oil fractions, one of the commonly used solvents is phenol, which has a preferential selectivity for the more aromatic constituents of the lubricating oil as compared to its more paraflinic constituents. The extracting of lubricating oil fractions with phenol has gained wide recognition as a highly desirable refiningstep. In general the process consists in treating the lubricating oil with phenol at a temperature atwhich the phenol is liquid whereby two layers of liquid are formed, the one layer, which is known as the extract, containing most of the phenol and the undesirable constituents that have been extracted from the lubricating oil, and the other layer, which is known as the railinate, consisting of the refined oil as well as some phenol. e The usual procedure for conducting the phenol extraction is to contact the 0'1 and the phenol in a countercurrent tower treating operation in which the oil, which is thelighter component,'is introduced into the bottom of the tower and the phenol, being the heavier-compo: nent',-is introduced into the top of the tower. The oil and phenol phases then flow countercurrently and come into intimate contact with each other, this contact usually being assisted by various contacting and distributing means. The pressure and temperature conditions for the extraction operation will depend upon the particular oil being treated, the volume of of oil being treated, and the quality of the desired product. In general the temperature will lie somewhere be tween the melting point of the phenol and the temperature at which complete m' ibility occurs between the oil and the phenol. The solvent-rich or extract phase will be removed from the bottom of the tower,.and the solvent-poor or rafiinate phase will be removed from the top of the tower.

In a phenol extraction process both the rafiinate phase and the extract phase contain dissolved phenol which must be recovered. This recovery involves considerable expense and contributes appreciably to the total cost of the solvent refining process. To recover the phenol the ratiinate and extract phases are usually heated to temperatures in the range of 450 to 750 F. to vaporize the phenol which can then be flashed oil. Additionally, for economical operation it is necessary to recover the remaining small quantities of phenol which are still present in the ratiinate and extract.- This isusually done by stripping the fractions with steam or with a suitable gas. In view of the expense involved in recovering phenol there is a need for increasing the etiiciency of extraction so that smaller amounts of solvent can be used thereby leading to reduced investment and operating costs for solvent recovery.

In accordance with the present invention, increased elliciency in phenol extraction is obtained by adding to the phenol a substance which will increase the solubility or the compounds that are to be extracted, which 1 tion tower 10 is provided solvent used per volume 1 1 water which 3,054,915 Patented Oct. 17, 1961 case of lubricating oil fractions means increasing the soluhydrocarbons and particularly the polycyclic aromatics. This is accomplished by adding to the phenol a nitrophenol or nitrocresol whose acidity is greater than phenol. Such nitrophenols or nitrocresols are those whose nitro groups are in either the ortho or the para position relative to the hydroxy group. These nitrophenols are selected from the group consisting of orthonitrophenol, paranitrophenol, 2,4-dintrophenol, 2,6- dinitrophenol, and 2,4,6-trinitrophenol or the corresponding cresols. The nitrophenol compounds are employed in the proportion of from 1 to 25 percent by weight based on the phenol. A range of from 5 to 15 percent is preferred. The particular percentage used will in large measure depend on the amount of polycyclic aromatics in the mineral oil fraction being extracted.

The nature of the invention will be more readily understood when reference is made to the drawing in which the single figure is a schematic flow plan of a process for conducting the phenol extraction.

Referring specifically to the drawing a phenol extracwhich may be packed with suitable contacting material such as Raschig rings, baffie plates or disc and donut plates. Preferably the contacting means comprises a plurality of underflow weir trays. The lubricating oil fraction to be treated enters through feed line 11 and is heated to the proper inlet temperature by means of heat exchanger 12. Phenol enters the extraction tower through phenol line 13 and flows downwardly through the tower so as to effect countercurrent contact with the upflowing lubricating oil. The oil that has been contacted with the phenol leaves the top of the tower as a raiiinate phase through line 15, is heated in a heater or furnace 16 and is then sent to a raffinate recovery tower 20. Similarly the extract phase leaves the bottom, of the extraction tower through line 17 and passes through heater or furnace 18 and is sent into an extract recovery tower 30.

The phenol employed in this extraction is, of course, the phenol that has been modified by the addition of a nitrophenol, as mentioned above. The previously prepared blend of phenol and nitrophenol may be introduced through line 13 or alternatively a properly proportioned stream of the nitrophenol may be introduced through line 14. Line 14 may also be employed for the introduction of a small proportion of an anti-solvent such as is common practice in phenol extraction. Thus, from 0.1 to 5 weight percent of water, based on the phenol, may be used.

Preferably the extraction in tower pressure, using pressures of from about 50 to about 10 is run under 250 1 p.s.i.g., so that the raffinate phase and extract phase will inthe each flow to its respective recovery tower without further pumping. Means for controlling this operation include flow control valve 21 in line 15, which is adjusted to maintain the desired phenol-oil interface in the extraction tower, and back-pressure control valve 22 in line 17, which. serves to regulate the flow of extract phase from the tower. Pressure operation in this manner eliminates the need for the surge drums conventionally employed in phenol extraction plants to receive the extract and raffinate phases prior to further handling, as well as the boosterpumps conventionally used to send these phases to their respective recovery systems.

In raffinate recovery tower 20 the phenol solvent is extracted from the raifinate by means of steam or other stripping gas, such as propane, which is introduced through line 26. Tower 20 may include one or more stripping and/or rectifying zones containing beds of suitable contacting surfaces such as rings or bubble cap plates. The upper portion of tower 20 may contain a rectifying zone for the condensation of oil that has been a 4. V t vaporized in the furnace and in the lower stripping zones proved the selectivity for removal of S-ring and 4-ring of the tower. A mixture of stripping gas, phenol vapors, aromatics. nitrophenol vapors, and traces of oil will leave the tower Table I V extraction process.

through line 28 while the stripped rafiinate will be recovered by means of line 29. V Phenol The extract recovery tower 30 likewise includes a P118110 r r 2-R1ng 1.3 1.2 tower and .flow back into the lower stripping zone. A 3-Ring 1. 8. 3.8 suitable stripping gas is introduc v Stn in gas and phenol and. mtrop enol vapors leave a the t ow r through line.32 While stripped extract leaves; 80%phem]; 20%ethy1emg17m1f. t the tower through line33. Thephenol and nitrophenol The separation factor is a measure of the selectivity in the effluent gases in lines Y28 and 32 are of course of theextraction, and is calculated as the volume ratio of recovered by means not shown to be used again in the agiven compound .(e.g., the 2-ring aromatics in this case) to a vkey compound (-l-n'ng aromatics in this instance) In the event that the particular nitrophenol cannot be in the extract phase, divided by the same ratio in the completely recovered by the flashing and stripping operraflinate. The increase in the separation factor for 3- ation described, or in cases where the economics are and t-ring aromatics with the addition of .dinitrophenol more favorable for doing so,' the operation may be augshows anincreased selectivity for .these types. Furtherhne 33 may be sent via line 34 to a wash zone 35 where constant hydrocarbon solubihty indicates that the d1- the remaming mtrophenol is removed by water washing. nitrophenol 15 not actlng simply as an anti-solvent such The washed oil is recovered in line 36 and the wash as .water,;glycol, etc. It isrreally acting to promote more water'is conducted via line 37 to distillation zone38 to '25 solution of these aromatics presumably due to the fact separate water and nitrophenol via lines 39 and 40. 7 that molecular complexes are formed' An alternative recovery procedure is to separate the g V phenolnitrophenol mixture 'by freezing it out of the oil. 7 EXAMPLE Thus the extract phase, .for example, may be conducted Aqueous phenol-(98%phenol and -2-% water) (solvent via line 41 to freezing zone 42 where it is chilled sutfi- 0 A) and amixture of 88 parts of that solvent with 12 parts ciently to crystallize out .the .phenol- .and nitrophenol. of 2,4-dinitrophenol (solvent B) were-compared for their The chilled mixture is then sent to filter 43 where sepasolvent extraction efliciency 1n the extraction of a medium ration of crystals from oilis effected, theseparated matedistillate naphthenic lubricating oil having a viscosity in rialthenbeing removed via lines 44and 45. a dex of 40, a viscosity at 100 -F. of 425 .SSU and an A.P.I. It is to .be understood that these alternate separation 35 gravityof 21.2. The extractions were conducted in the procedures are likewise applicable to the rafiinate phase. samemanner 'as'inExample :1. The ratfinate phase was The flow plans will be similar to those shown for the also washed with caustic and withwater, and the viscosity extract phase but have been omitted from the drawing of the washed sample was determined at 100 F. and at in order that the latter woul v not be unduly complex. 210 F. in-order to calculate the viscosity-index. There- The benefis derived from employing the modified suits obtainedaregiven-in TablelI.

solvent of the presentinvenion aredemonstrated by the V to separate. The extract phase waswashed withcaustic data obtained in theifollowing examples. 0 v V 7 Table H EXAMPLE 1 i .SolventA SolventB An aromatic blend was prepared consisting of a mix- 45 solv nt/on Ran g(vo1ume) ture of secondary .butyl benzene (33.9%) naphthalene a; 17.1%), phenanthrene 10.0% and py rene 5.2% viri 'tf i e iigfff mement" dissolved in normal dodecane (33.9%). (Allperc'entages Baflimtem oils 1 b." Et t, are y ght.) This blend was then extracted with on m basis for subsequent comparison with phenol to which iRafl.yield=loo% x\ x wo l oil recov. fr. extract onsolubm extract total extract volx'bet'ore washing as an antisolvent to avoid excessive solubility of the aromatics in the phenol. The extractions were made at T data-in Table t i f p conditions'alie' 75 F. using a single stage batch procedure wherein the adfiisted for ?"9 9 mime extract there oil and solvent were stirred for 30 minutes at the extracan Improvement m vlscoslty index over base case non temperature after which the phases were allowed What this means is that more selective extractionahas'been performed when usingsolventB. and then with water to remove phenol (andrnitrophenols ggz gg gfggg fifgggg ggi figg ging ky when they were used), and the amount of hydrocarbon these levelsrbeed b tr recovered was measured. With a 100% treat (lto .1 mg am jusmg'ex 911mm 1 solvent to oil volume ratio) the solvent containing the dinitrophenol gave a 33 volume percent hydrocarbon Table 111 solubility in the extract. For comparison the results without dinitrophenol from a 100% treat (giving 37 Rama 7 Avg v volume percent) and from a 150% treat v(giving 31 -HO'S01.inExt.;VoI. Percent Yield, Advantage volume percent hydrocarbon solubility) were interpolated a igh 3 5: to a 33 volume percent hydrocarbon solubility. The e results-of these tests are shown .in Table Iinterm's'of a separation factor relative to l-ring aromatics. The data indicate that, at 33 volume percent hydrocarbon solubility in the extract, the addition of the'dinitrophenol im- As the data in Table Hlshow, there is a considerable advantage in viscosity index when employing the solvent mixture of phenol and 2,4-dinitrophenol as compared with the phenol alone. From a practical standpoint, the V1.

gain be considered as an improvement in yield. Alternatively, the advantage in viscosity index can be intersolvent treat for a the mixed solvent. This is an imas pointed out above, solvent item in phenol expreted as requiring a lower intensity given V.I. when using portant advantage because, requirement is the most expensive traction.

EXAMPLE 3 In a manner similar to Example 2, the elliciency of a solvent mixture of 95 parts of the aqueous phenol and parts of 2,4-dinitrophenol (solvent C) was compared with the aqueous phenol alone (solvent A) in extracting additional quantities of the same lubricating oil and adjusting the temperature so that the same value of oil solubility in the extract was obtained in each case. The results are shown in Table IV.

modified solvent as compared to the base case at the same oil solubility in the extract.

EXAM LE 4 In the same manner as in Examples 2 and 3 the efiiciency of a solvent mixture of aqueous phenol with parts of orthonitrophenol was compared with that of the aqueous phenol. Additional quantities of the same lubricating oil were used as in the preceding examples. For comparison purposes an extraction was also made with a solvent mixture of aqueous phenol and 10 parts of 2,4- dinitrophenol. The results are given in Table V.

Table V Solvent Solvent Solvent A D E Solvent/Oil Ratio 1. 5 1. 5 1. 5 150 150 150 VI. of Raflinate 59 68 75 Oil Solubility in Extract, Vol. Percent" 23. 5 24 22 Solvent A-QS parts phenol, 2 parts water (weight). Solvent parts by weight 01 Solvent A; 10

onitrophenol.

Solvent E-QO parts by weight of Solvent A; 10 parts by weight 2,4-

dinitrophenol.

parts by weight By comparing the data obtained with Solvent D with the data from the base case (solvent A) it will be seen that at a constant oil solubility level in the extract phase, the addition of o-nitrophenol to phenol results in a higher viscosity index oil. The data obtained with solvent E indicate that o-nitrophenol and '2,4-dinitrophenol are roughly comparable in their effectiveness, with some advantage indicated for the latter.

While the invention has primarily been described with reference to the extraction of mineral lubricating oil fractions it is also applicable to the extraction of other relatively high boiling stock, particularly those that are likely to contain polycyclic aromatics. Such stocks include gas oils, heating oils, and catalytic cycle stocks, for example.

.Also, while the above examples have primarily illusdated the separation of hydrocarbons of difierent types from each other, the invention is also applicable to the removal of non-hydrocarbon constituents from. mineral oil compositions.v This is shown by, the following example. g

EXAMPLE 5-; V

A blend of the following constituents was prepared: dodecane (50%), secondary butyl benzene (30%), dibutyl sulfide (5%), dibenzothiophene (5%), indole (5%), and quinoline (5%), all percentages being by weight. In the manner of Example 1, portions of this blend were then extracted at various treat levels with a modified phenol consisting of weight percent phenol and 20 weight percent ethylene glycol, using an extraction temperature of 72 F. A portion of the blend was also extracted at a 100 percent treat level with a mixture of weight percent of the modified phenol and 10 2,4-dinitrophenol. Under these conditions hydrocarbon solubility in the extract with the latter mixture was 22.5 volume percent. The results for extractions with the phenol-glycol solvent at 18% and 28% hydrocarbon solubility in the extract were interpolated to 22.5 volume per cent and the results compared with those for the solvent containing the dinitrophenol. The

separation factors relative to second butyl benzene are presented in Table VI.

Table VI Sep. Factor Relative to Secondary Butyl Phenol Phenol Benzene 10% DN? Dibutyl Sulfide l. 5 l. 3 Dlbenzothiophene- 3 4. 4 Indole 7 9.0 Quinoline 17 24. 5

1 80% phenol; 20% ethylene glycol.

It will be noted from the data in Table VI that the modified solvent gave a marked improvement in the extraction of dibenzothiophene, indole, and quinoline. This is of considerable significance because materials of these types con 'bute to poor color and poor oxidation stability in mineral oil compositions. Hence methods for their removal are in demand.

Other variations of the invention within its scope and spirit are also contemplated; accordingly the invention is not limited to the specific embodiments herein described. Its scope is to be determined by the appended claims.

What is claimed is:

1. A process for treating a mineral oil fraction which comprises contacting said oil with a selective solvent comprising phenol and from about 1 to about 25 weight percent, based on the phenol, of a nitrophenol selected from the group consisting of ortho-nitrophenol, paranitrophenol, 2,4 dinitrophenol, 2,6 dinitrophenol, and 2,4,6-trinitrophenol.

2. Process as defined by claim 1 wherein from about 5 to about 15 weight percent of the nitrophenol is employed.

3. Process as defined by claim 1 wherein said petroleum oil comprises a lubricating oil fraction.

4. Process as defined by claim 1 wherein said nitrophenol comprises 2,4-dinitrophenol.

5. Process as defined by claim 1 phenol comprises ortho-nitrophenol.

6. A process for treating a lubricating oil stock which comprises contacting said oil with a selective solvent comprising 88 parts of a mixture consisting of 98% phenol and 2% water, and 12 parts of 2,4-dinitrophenol, separating an extract phase which contains the phenol solvent mixture and undesirable polycyclic aromatics and a rafliniate phase consisting of the refined oil.

7. A process for treating a lubricating oil stock which wherein said nitroeomprisesbontactin'g said oil with a selective solvent com Referencsfiited in the file o'f this pate'nt pris ing'8 8 parts (of-a mixture :consistingof 98% phenol I Q. k V v and 2% wafer," and 10 parts 0f ort honitropheno'l, separat I I UNITED STATE-S i 1 7 ing an extract phase'which contains the phenol solvent 2,1 8,958 r I Ctmradrebal. r-----Y-" CP 6, v1938 mixture and undesirable polycyclic aromatics and a 5 1 5 G SP July- 9, :19 1

raflinate phase eonsis g of the refined oil. 7 9 5 AXQ --7--------'--- y 

1. A PROCESS FOR TREATING A MINERAL OIL FRATION WHICH COMPRISES CONTACTING SAID OIL WITH A SELECTIVE SOLVENT COMPRISING PHENOL AND FROM ABOUT 1 TO ABOUT 25 WEIGHT PERCENT, BASED ON THE PHENOL, OF A NITROPHENOL SELECTED FROM THE GROUP CONSISTING OF ORTHO-NITROPHENOL, PARANITROPHENOL, 2,4 - DINITROPHENOL, 2,6 - DINITROPHENOL, AND 2,4,6-TRINITROPHENOL. 